The Plasticity of Animal Fibres
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108 SPEAKMAN AND SHAH-THE PLASTICITY O F ANIMAL FIBRES April 1941
ready for the second lot of colours and so on until the goods are passed forward for the finish- ing operations.
Rainbowing-Another type of hand block printing is known as rainbow printing; it i s the method adopted when the colours are intended to run into one another, and differs only from ordinary block printing in the means employed for furnishing the sieve with colours. This is done by a special colour lyter that deposits the various colours in little pools across the width of the sieve; these colour pools are then spread as stripes across the sieve.
The colour lyter consists of a length of wood the same size as the colour box. On one side of the board is a handle and on the other a series of adjustable pegs so arranged that when they are dipped into a divided colour box, each peg falls into a specific compartment and then takes up its own particular colour. During printing, the block works against gauges to ensure that it is always dipped in the same place on the sieve.
(The Lecture was illustrated by a very fine collection of block-printed fabrics in various sfages of completion.)
The Plasticity of Animal Fibres J. B. SPEAKMAN
When animal fibres are deformed, the main peptide chains undergo rearrangement against the attractive forces between neighbouring peptide groups, the positive and negative ions of salt linkages, and the resistance offered by the co-valent cystine linkages. If a fibre is retained in a state of deformation, the internal stress is dissipated by rearrangement of the molecular structure, nt a rate which increases with increasing relative humidity and temper- ature. I n steam, or in water at high temper- atures, the decay of tension is facilitated by disulphide bond breakdown, which is succeeded by the formation of new linkages between the peptide chains. These new linkages impart a permanent set to the deformed fibre, and in the detailed study of setting processes which has been described in previous papers, the influence of various reagents and the pH of the setting medium on the set acquired by the fibre has been fully examined.
Despite the importance of the subject, however, the rate of decay of tension in strained animal fibres a t low temperatures has received little consideration since the publication of preliminary observations1 in 1028. The ability of strained animal fibres to dissipate stress without change of shape, and without neces- sarily losing their ability to return to their original form when released in water, has important practical significance and may be either advantageous or not according to the particular process under consideration. It is turned to advantage in the storage of tops, where stresses retained after carding and combing are given time to decay prior to drawing and spinning; but it is clearly a dis- advantage in the case of hard-twisted yarns intended for use in the manufacture of wool cr6pes. With such considerations in mind, it was decided to amplify the earlier study of the plasticity of wool, particularly as regards the
and S. Y. SHAH influence of the temperature and p H of the medium on the rate of decay of tension in strained animal fibres. Although the experi- mental work was carried out with stretched fibres, the results are capable of qualitative application to deformed fibres in general.
EXPERIMENTAL Hunian hair waa preferred for use in the
experiments because of the uniformity of diameter of the fibres along their length. As usual, the hair was purified by extraction with alcohol and ether successively in a Soxhlet apparatus, followed by washing in distilled water,and the intact root ends of non-medullated fibres were selected for experiment,.
The apparatus used to determine the rate of decay of tension in strained fibres is shown in Fig. 1.
It is similar to that used in earlier work and consists epentially of a heavy brass base supporting two vertical pillars, midway between which turns a calibrated brass screw of 1 mm. pitch. A traveller T , carrying a calibrated steel spring S, slides along the pillars and is
April I941 SPEAKMAN AND SHAH-"THE PLASTICITY O F ANIMAL FIBRES" 109
actuated by turning the screw. The number of turns made by the latter is indicated by the pointer P, which moves over a dial graduated in degrees. Below the spring S is a cylindrical glass tank cemented to the metal base, through which the plunger L, carrying a hook at its upper end, is operated. A glass lid, cut in half, closes the tank, with the exception of a pinhole in the centre immediately above the hook of the plunger. The whole apparatus was built into a thermostat, the water of which came almost up to the level of the top of the glass tank.
The method of using the apparatus was as follows-by means of sealing wax or dental cement, according to the conditions of the experiment, a 5-cm. length of fibre was attached to two light glass hooks, one of which was looped in the middle as shown in Fig. 1. After oalibrating the fibre, by measuring the major and minor axes of the elliptical cross-section a t intervals along the length in an atmosphere a t 65% R.H. and 22.2" C., a needle was inserted through the loop, and the lower hook engaged with the hook of the plunger. The spring S , having a sensitivity of 0.575 mm./g., was then lowered and engaged with the upper hook, which moved freely upwards within the pinhole of the lid. After measuring its unstretched length by means of a reading microscope, the fibre was extended rapidly by withdrawing the plunger to the required extent, which was determined by a stop placed underneath the tank, The spring was then extended by turning the pointer P to raise the traveller until the upper hook attached t o the fibre was seen to lift slightly from the needle. A measure of the tension within the fibre at this moment was, of course, given by the number of revolutions of the pointer P which determined the extension of the spring. If the system were then left untouched, the fibre would extend and the spring contract. To obviate extension of the fibre, and follow the rate of decay of tension a t constant length, the spring was caused to contract by making half turns of the pointer a t intervals, and the times were noted at which the upper hook, as observed through a micro- scope, lifted from the needle. At the end of the experiment, the length of the spring was measured by means of a travelling microscope, and its length at any previous time was cal- culated from the known number of half turns which had been made. The stretched length of the fibre was also determined.
(1) The Rate of Reluxation as a Function of Fibre Externion-In these experiments, fibres were stretched different amounts in distilled water a t 25" C., and typical curves illustrating the decay of tension at different (constant) extensions are shown in Fig. 2.
Unfortunately, only empirical equations were found to fit the curves, but a convenient indi- cation of the rate of decay of tension is given
- 1.0 0.0 I .o 2.0 3.0 Log Time In Mln.
by the half-tension time, which is defined as the time needed for the tension at 1 min. after extension to decay to half its value. The data obtained are given in Table I, illustrated by Fig. 3.
(%) 7.3 4.00 x i n 5 9.4 13.5 18.8 23.1 28.0 34.7 37.8 41.6 46.7
. . . . . . 4.30
G.84 ,, 0.76 ,, 10.50 ,, 11.05 ,, 11.25 11-50 ::
4.58 " 4.75 ::
76.2 34.8 14.86 7.20 4.80 3.40 1.87 1.82 1.07
$ 60 C
E 8 F 40
1 3 20 I
0 0 10 20 30 40 so
S: Extension BIG. 3
At low extensions, where the amorphous phase of the fibre is primarily affected, the rate of decay of tension is small, but a t extensions above 23% approx., where the crystalline phase begins to undergo conversion from a- into /?-keratin, the rate of decay of tension is high. To some extent this peculiarity is due to the fact that a critical stress of about 3.7 x 106 g./cm'.,
110 SPEAKMAN A N D SHAH-"THE PLASTICITY O F ANIMAL FIBRES" Apr i l 1941
representing a high proportion of the total stress a t low extensions, is required to overcome the van der Waals attractive forces before the main peptide chains can unfold. All further experiments were, therefore, carried out with fibres at relatively high extensions, in the neighbourhood of 40%.
The Rate of Relaxation as a Function of l'evnperature-Fibres were stretched 40% in distilled water a t temperatures ranging from 25" C. to 95" C., and curves illustrating the rate of decay of tension at constant length are given in Fig. 4.
- 1.0 0.0 1 .O 2.0 3.0 Log Time in Min.
The values for the half-tension time, which are given in Table 11, are shown as a function of temperature in Fig. 5.
TABLB I1 ~~ ~ __ - ~
25.0 30.4 47.0 56.8
74% 85.3 95.0
41.5 39.3 39.3 39.2 38.2 40.3 42.2 42.2
1 1 . ~ 2 x 105 8.11 ,, 8.20 ,, 7'10 ), 8.26 ,, 3.86 ,, 2.53 ,, 1.10 ,,
105 03.1 41.7 14.4 7.0 3.7 2% 3.8
As is to be expected, the half-tension time decreases rapidly with rise of temperature, but little advantage is gained by raising the temper- ature above 60" C., although, of course, the magnitude of the internal tension at correspond- ing times decreases steadily with rise of temperature up to 100" C. The higher value for the half-tension time at 95.0" C. , as compared with 85.3" C., is due simply to the fact that each value of half-tension time is based on the tension at 1 min. after extension, and the decay of tension during this first minute is
considerable in water a t high temperatures. In view of the fact that fibre relaxation is
i f 80
c - 60
z .' 40 u
0 20 40 60 80
promoted by disulphide bond hydrolysis, it is interesting, and, to some extent, surprising that there should be no abrupt change in the half-tension time at temperatures above 40" C . , a temperature which has been found to be critical in other types of experiment2.
The Rate of Relaxation as a Function of the p H of the Medium-In this case, the fibres, after being immersed in the buffer solutions for at least 1 hr. a t 25" C., were stretched 40% and allowed to relax. Typical curves, illustrating the rate of decay of tension at different pH values, are shown in Fig. 6.
x I06 1 I I I
0 I - 1.0 0 .o I .O 2.0 3.0 Log Time in Mln.
Values for the half-tension time, and details of the buffers employed, are given in Table 111.
April Ifid1 SPEAKMAN AND SHAH-"THE PLASTICITY OF ANIMAL FIBRES" 111
TABLE 111 . _ _
precise range of the stability region is, however, dependent on the nature of the buffers used. Experiments similar to the preceding were carried out with McIlvaine's citrate buffers a t 25" C., and the resulting data are given in Table IV, illustrated by Fig. 7.
40.0 41.0 40.8 40.5 40.7 40.5
._ ~~~ ~- Tenalon at
Log of half-
2.04 1.94 2.03 1.99 1.72
- 40.8 3 9 4
-- BCl+KCI ._. ...I 1.07 BC1 + KCI ... ... 2.02
NaOH + ''-COOK 4.09 (I-COOH 1
10.09 x lo! 10.59 ,,
1 0 4 1 ,, 10.81 ,, 11.30 ,. 10.18 ,, 10.41 ,, 9.03 ,, 8.34 ),
8.03 ,, 3.38 ,,
TABLE IV - ~- _ _ -
Extension Tension at 1 i i h . Log of half-tension (%) 1 (g./crnJ initial arca)j time in inin.
2.14 3.03 4.08 5.03 8.00 8.98 8.02
- ~ ~~~~
10.95 x 105 11.02 ,, 11.31 ,, 11.40 ,, 12.44 ,. 11.49 .. 10.74 ,,
2.88 2.85 2.26 1.90 14U 1.84 1.85
NaOH NaOH NaOH NaOH NaOH NaOH
+ KHzP0.q ... + KHzPO+ ... + HjB03 ..., + HjBOj + HjBOj :::I + NHzCHzCOOH In this case, the stability region extends from
pH 5 to 8, compared with pH 6 to 9 in the preceding experiment, and the half-tension time in the stability region is less than before. While the appearance of a stability region seems, therefore, to be independent of the nature of the buffers used, its range and location are not, possibly because of variations in the degree of swelling of the fibre.
(4) The Rate of Relaxation as a Function of Fibre Swelling-The striking extent to which the rate of relaxation is modified by depression of swelling is well shown by the data of Table V. Buffers which had been saturated with sodium chloride a t 22.2" C. were used, and the fibres, after overnight immersion in the solutions, were stretched at 26" C.
The half-tension time is shown as a function of the pH of the buffer solution in Fig. 7.
+-+-+ Mixed Buffen + NaCl O--O-O Mlxed Buffers X-X-X Citrrte Buffera
t z - c 3 E $ 1
P I s"
tenalon ~ half-
Tension at 1 miu.
1248 x 105 1168 ,, 15.50 ,, 13.19 ,, 14.33 11.47 ::
p H after
siou (%) time
1 in min. I .. 1 3.50
3.22 2.76 2.79 2.46 1.98
39.6 4.42 0 2 4 6 a 1 0 12 PH
Above pH 9, the half-tension time decreases rapidly with rise of pH owing, no doubt, to disul- phide bond h ydrolysisand associated phenomena. Conversely, the low rate of decay of tension a t low pH values seems to be due to the stability of the cystine linkage in acid media, as is exemplified by the fact that cystine may be isolated from the hydrolysates which are obtained when wool is boiled with 20% hydro- chloric acid. Between pH 6 and 9, however, the half-tension time is sensibly independent of the pH of the buffer, and i t is tempting to suppose that this stability region is determined by the properties of the salt linkages. Besides being stable between pH 6 and 7 in buffer solutions, the salt linkages show little affinity for alkali below pH 9, and it is possible that the distribu- tion of stress within the molecular structure depends on whether the salt linkages are intact or broken when the fibre is stretched. The
. .- 6.58 7.00 8.00 8.90
40.4 40.5 39.8 40.8 39.3
At any given pH value, both the initial tension and the half-tension time are increased when the buffer contains added salt, but the range of the stability region, as shown in Fig. 7, is consider- ably reduced. The increase in initial tension must, of course, be attributed to reduced swelling, which, because of the high salt con- centmtion, is due to the reduced relative humidity of the buffer solution as well as to reduced osmotic swelling. As is indicated by the results given in a previous paper', any increase in the initial tension, due to a fall in relative humidity, is accompanied by an increase in the half-tension time, so that the increased values of half-tension time given in Table V are not unexpected. The fact that the ra,te of relaxation is so strongly affected by depreasion of swelling makes it difficult to interpret the existence of a
112 SPEAKMAN AND SHAH-"THE PLASTICITY OF ANIMAL FIBRES" April 1041
Tendon [g./em!initlal area)
11.23 X 105 10.81 ,, 10.40 ,, 9.98 ,, 9.57 ,, 9.15 ,, 8.73 ,, H.32 ,, 7.83 ,, 7.50 ,, 6.87 ,, 6.37 6.14 ,, 5.92 ,, 5.81 ,.
stability region when buffers of varying com- position and swelling power are, of necessity, used, but the reduced range of the stability region in solutions containing excess salt must be due, in part at least, to the effect of the salt in minimising the difference between the internal pH of the fibres and the pH of the medium.
Although the depression of swelling has such a marked effect on both the initial tension and the half-tension time, increased swelling, when produced by concentrated solutions of weak acids, is without significant effect. For example, the increase in the average lateral dimensions of human hair fibres, on transference from distilled water to 5~-monochloroacetic acid at 22.2" C., was found to be lS .O~o , compared with 1.80/, for 0.3 N-hydrochloric acid, the pH of both solutions being 0.70. Despite this striking difference in the degree of swelling, fibres stretched in the two media a t 25" C. gave almost identical rates of decay of tension, as is shown by the data of Table VI, illustrated by Fig. 8.
I IIydrochlorlc aeld
Extenslon of Rbre - 39.8% ' I Monochloroacetlc add Extenslon of flbre = 41.3%
T i m (niln.)
0.407 0.80 2.10 4.85
10.25 21.7 43.5 91.5
1376 1765 2815 4255 5670
0.367 0.76 2.50
325 1500 4380 7190
l l .H8 x 105 11.08 ,, 10.28 ,, 9.48 ( ( 8.08 ,, 7.88 ,, 7.08 ,, 0.04 ,, 5.48 ( (
3--0--0 CHzCI.COOH X I 0 x-x-x HCl
- 1.5 0.5 I 4 2.5 3.5
The action of concentrated solutions of weak acids is to separate the sheets of co-valently- linked peptide chains against van der Waals
Log Time In Mln. FIQ. 8
attractive forces, but the tension required for 40% extension of the fibre is almost unaffected by the process. It is not surprising, therefore, that the rate of decay of tension in th-mono- chloroacetic acid should be similar t o that in 0.3 N-hydrochloric acid, especially as the effect of swelling on both the magnitude of the initial tensionandits rate of decay must be greatest in the initial stages of swelling.
The preceding results are more helpful in interpreting the existence of a stability region than might at first sight appear. Although swelling depression has such a marked influence on both the initial tension and its rate of decay, a higher half-tension time is accompanied by an increased internal tension (compare Table V with Tables I11 and IV). There is, however, no correspondence of initial tension and half- tension time over the stability region in Tables I11 and IV, and it seems clear that while the range and precise location of the stability region may be dependent on the salt content and constitution of the buffer, there is in fact a true stability region independent of these factors. Its origin may be connected, in part, with the fact that, within the range of pH where salt linkages are stable, their positive and negative ions, separated during fibre extension, impede internal molecular rearrangement and decay of tension by their mutual attraction. Outside this range, the decay of tension is promoted to an extent which increases with the degree of salt linkage breakdown, but the function of the salt linkages is there masked by the instability of cystine linkages in alkaline solutions and their stability in acid. Such behaviour of the salt linkages, combined with their effect in modifying, when intact, the distribution of stress within the fibre, may suffice to explain the existence of a stability region. The further possibility that the cystine linkage, which is unstable in alkali and stable in acid, may itself be unaffected by variations in pH within the stability region is one which requires separate investigation by a different technique. It will receive further discussion in a later paper.
The importance of salt linkages in determining the rate of decay of tension seems to receive support from the results of earlier experiments, where it was found that the half-tension times of deaminated, acid-dyed, and formaldehyde- treated fibres, particularly the first, are greater than the half-tension time of untreated fibres in distilled water a t 25" C. Such results are not, however, conclusive. The lower rate of decay of tension in the case of deaminated fibres may be connected with side reactions, perhaps even with cross-linkage formation, since such fibres cannot be stretched more than about 36% without rupture. Cross-linkage formation certainly occurs when fibres are treated with form- aldehyde, and the higher half-tension time of acid-dyed fibres may be due to the action of large dye molecules in impeding molecular
April 1941 SPEAKMAN AND SHAH-"THE PLASTICITY OF ANIMAL FIBRES" 113
0.433 0.76 1.08 1.80 3.20
6.75 0.00 14.03 28.00 622 102.0 317.0
rearrangement. It is thus extremely difficult to devise conditions which will reveal the true function of the salt linkages, and the following experiment was no more successful than those with chemically-treated fibres. A fibre was stretched 40% in distilled water at 26" C . , and the rate of decay of tension followed for a few minutes. The water was then replaced by a solution of hydrochloric acid (pH = 1.06) at 26" C., with continuous observation of the rate of decay of tension. From the resulting data, which are given in Table VII, illustrated by Fig. 9, it is evident that the tension within the fibre undergoes no abrupt change when water is replaced by hydrochloric acid.
12.07 X 106 11-56 ,, 11.06 ,, 10.54 ,, 10.04 ,, 9.30 ,, 0.06 ,, 8.54 ,, 8.03 ,, 7.63 ,, 7.08 ,, 6.60 ,, 6.42 ,, 614 ,,
aced by HCI
Tension Time 1 (min.) (g . /cd initialarea)
1 I I I - 1.5 0.5 I 3 2.5 3.5
Log T h e In Mln.
W O . 9
The half-tension time is about 1040 min., compared with 110 min. for a fibre a t 40% extension in water throughout, and the effect of acid on salt linkages is, as might be expected, masked by increased stability of the cystine linkages.
( 4 ) The Rate of Relaxation in Solutions of Sodium Sulphite and Sodium &fetabi8ulphite- The increased rate of decay of tension in strained fibres in solutions a t pH 9 and above has been referred to disulphide bond hydrolysis. Support for this view is to be found in the behaviour of strained fibres in solutions of sodium sulphite
and sodium metabisulphite, which are known to cause disulphide bond breakdown. After calibration, each fibre was immersed in the appropriate solution for 16 hr. before being stretched 40% at 26" C. Besides containing 6% by volume of alcohol as antioxidant, the solutions of sodium sulphite and sodium bisulphite, each of N-concentration, were satu- rated with sodium chloride a t 22.2" C., with a view to depressing fibre swelling and isolating the simple effects of disulphide bond breakdown. For purposes of comparison, however, one experiment was carried out with N-ROdiUm sulphite solution containing no sodium chloride. Curves illustrating the rates of decay of tension given by the various reagents are shown in Fig. 10, the resulting data being summarised in Table VIIJ.
Tenelon at Log of
Reagent I pII 1 (%) 1 (g./cn? I tlmeln lnitlal area) mln.
NazSO3 ... 10.08 40.5 2.87 x 106 0.82 NazS03+ NaCl 8.90 40.2 10.26 1.29 NnHSOj+ NaCl 3.68 1 40.0 1 4.93 :: I 1.43
5 , z .- e .-
"$ 6 5 - E 4 f
O--O--O NazSO3 x-x-x NazSOj+ NaCl
lo5 +-+-+ NaHSOz+ NaCl
-1.0 0' 0.0 I .o 2.0 Log T h e In Mln.
Even in presence of sodium chloride, relaxation takes place with great rapidity in solutions of sodium sulphite and sodium bisulphite, thus confirming the important part played by disulphide bond breakdown in causing relaxation. It is interesting to note that both the initial tension and the half-tension time are less in sodium sulphite-sodium chloride solution than in boric acid-oodium hydroxide-sodium chloride solution (Table V) at the same pH value of 8.90.' This result suggests that, with strained disulphide bonds a t least, sodium sulphite does not react
114 EXTERNAL ADDRESS April 1941
as a simple alkali, but more probably according to the equation- R-S-S-R + Na,SO, = It-SNa + R-S-S0,Na
SUMMARY Because of its importance in relation to
various processes, the relaxation of strained animal fibres has been studied as a function of fibre extension and the temperature and pH of the medium. In distilled water a t 25" C., the rate of relaxation increases with increasing cxtension of the fibres, and, a t a constant extension of 40%, with increasing temperature up to 60" C., beyond which little further change takes place. Rapid relaxation can, however, be brought about a t low temperatures (25" C.) by means of agents such as alkalis, sulphites and bisulphites, which are known to cause disulphide bond breakdown. Conversely, the rate of relaxa- tion is least in solutions of simple acids, e.g.
hydrochloric acid at pH 1 , where the disulphide bonds are stable. Of less importance are the aalt linkages, but they may be responsible for the existence of a region, which varies in extent according to thc nature of the buffers used, within the range pH 5 to 9, where the rate of decay of tension at 25" C. is sensibly independent of pH. Whatever the pH of the medium, however, the rate of relaxation can be reduced by depressing the swelling of the fibres, e.g. by means of sodium chloride. TEXTILE CHEMISTRY LABORATORY
(Received on 10th February, 1941) LEEDS UNIVERSITY
REFERENCES Speakman, Proc. Roy. Soc., 1928, IOSB, 377. Speakman, Stott, and Chang, J. Texti le Inst . , 1933,
24, "273; Speakman and Smith, this Jour., 1936, 62, 121.
EXTERNAL ADDRESS Science, National and International, and the Basis of Co-operation
A. V. HILL It is generally admitted that the nature
of their occupations makes scientific men particularly international in their outlook. In its judgrncnts on facts science claims to be independent of political opinion, of nationality, and of material profit. It believes that Nature will give a single answer to any question properly framed, and that only one picture can ultimately be put together from the very complex jigsaw puzzle which the world presents. Individual and national bias, fashion, material advantage or a temporary emergency, may determine which part of the puzzle at any moment is subject to the greatest activity. For its final judgments, how- ever, and for its estimates of scientific validity, there is a single court of appeal in Nature itself and nobody disputes its jurisdiction. Those who talk, for example, of Aryan and non-Aryan physics, or of proletarian and capitalist genetics, as though they were different, simply make themselves ridiculous. For such reasons, the community of scientific people throughout the world is convinced of the necessity of inter- national collaboration ; has practised such collaboration for many years, indeed along tho centuries, and has built up an elaborate system of congresses and unions of standards, units and nomenclature, and of abstracting journals, together with a widespread interchange of research workers and ideas from one country to another.
In no other form of human activity, therefore, has so complete an internationalism spread throughout the national structure of society; in no other profession or craft is there so general an understanding or appreciation of fellow
workers in other parts of the world. This implies no special merit or broadmindednrss on the pat of scientific men; it is their very good fortune, a good fortune which involves obligations as well as privileges. For example, when the Nazis in 1933 began their persecution of Jews and liberals in Germany, it was the scientific communities of mimy other countries which came most quickly to the rescue of their colleagues; not out of any spccial generosity, but because Jirstly, they had personal knowledge of thosc who were being persecuted, and secondly, they realised that such persecution struck at, the basis of the position of science and scientific workers in society. Again in the treatment of aliens in this country during the present war, the scientific community more than any other, and quite rcgardless of political complexion, has stood for a liberal and reasonable policy; desiring both to maintain the high tradition which thc world of learning has inherited from the past, and also to make use of thc willing help of people whom it knew personally to be loyal to the cause of freedom for which i t is at> war. Again, in the Urited States to-day, t,here is no section of the public so unanimously concerned for the victory of British arms as the community of university, and particularly of scientific, people. These realise that the basis of all progress in science and learning is international ro-operation, and they cannot ccnceive how such co-operation could be possible under a Nazi domination of the world.
It is possible, therefore, that through this by-product of international ro-operation, science